Once you have your account set up, tap the menu at the top left. Then tap on the Settings (gear) icon.
Swipe down and you'll see a link that says "Invite another family"
Then complete the invite screen (below) and tap Invite family to Stretch.
Your contact, in this example firstname.lastname@example.org, will receive an email invitation from you. Bill can accept the invite, set up his (or her) family, and join your Tribe.
Voila! Instant family network!